Corrugated thermoplastic articles



Nov. 24, 1970 P. H. PARKER CORRUGATED THERMOPLASTIC ARTICLES Filed April 5, 1968 INVENTOR PH/LL/P H. PAR/(ER AT T RN EYS United States Patent O 3,542,635 CORRUGATED TH RMOPLASTIC ARTICLES Phillip H. Parker, San Rafael, Calif, assignor to Chevron Research Company, San Francisco, Calif., a corporation of Delaware Filed Apr. 5, 1968, Ser. No. 719,147 Int. Cl. B3211 3/10 US. Cl. 161109 10 Claims ABSTRACT OF THE DISCLOSURE FIELD OF THE INVENTION This invention concerns corrugated thermoplastic articles made from uniaxially oriented sheets of substantially crystalline polymer and methods for preparing such articles.

INVENTION DESCRIPTION The corrugated thermoplastic articles of this invention comprise at least two uniaxially oriented sheets of substantially crystalline polymer. The sheets are cross lapped at an angle of at least about 10 relative to their directions of orientation, perforated in closely spaced, parallel rows and fusion bonded a the peripheries of the perforations. Each row of perforations runs approximately along the bottom of the corrugation grooves.

Thermoplastic polymers which are useful in this invention include orientable, normally solid, substantially crystalline poly-l-alkenes such as polypropylene, polyethylene, poly-l-butene and poly-4-methyl-l-pentene, polyesters, and polyamides, polyvinyl chloride, polystyrene polycarbonates and the like. The term polymers as used herein includes copolymers and physical mixtures of the above-described thermoplastics. Poly-l-alkenes of monomers f 2 to 6 carbon atoms are preferred. Polypropylene is particularly preferred. If sheets of diflerent polymers are used, they must be fusible thermally.

The general technology for preparing the sheets used in this process is well known in the art. The substantially crystalline polymer is extruded in a conventional extruder to provide a sheet or film of desired thickness and width. These sheets or films have substantially uniform thicknesses. The film is then oriented uniaxially by stretchingit in one direction at elevated temperatures. The stretch temperatures will depend on the polymer used. The film may be heated to the desired temperature by passing it through a heating zone or over heated rolls or drums. It may be stretched in a single step or in a plurality of steps. The draw ratios used to orient the film will normally be in the range of about 4:1 and the ratio which causes the film to fibrillate spontaneously. This latter ratio again will depend upon the particular polymer involved. For the preferred polymer, substantially crystalline polypropylene, draw ratios between about 6:1 and 12:1 will be used. Preferably the oriented sheet or film thickness will be in the range of about 0.5 and about mils.

The sheets are positioned such that their orientation directions are not parallel but are rotated at least about relative to eachother. In other words they are positioned so that their lines of orientation intersect at an angle of at least about 10. Such positioning gives the corice rugated article better lateral strength than if the lines of orientation of the sheets were aligned parallel. Preferably the sheets are rotated at approximately to each other.

While articles containing any number of sheets may be prepared, articles made with two to four sheets will be most common. Articles made with two sheets are preferred.

The shape of the perforations is a practical rather than a critical variable. They may be square, oblong, triangular, rectangular, circular, etc. They will normally be circular. These circular perforations will usually be about 0.01 to about 1 inch in diameter. As regards the spacing of the perforations, adjacent perforations in a row will normally be about 0.1 to about 3 inches apart and the rows of perforations will normally be about 0.1 to about 3 inches apart. Preferably, the distance between adjacent rows and the distance between adjacent perforations in a row will be substantially the same.

The articles of this invention are made by first placing two or more thermoplastic sheets in intimate contact at an angle of at least about 10 relative to their directions of orientation. The films are then perforated simultaneously with a sharp element, such as a needle, heated to at least about the fusion temperature of the thermoplastic. For polypropylene the elements will usually be heated in the range of about 300 F. to about 600 F. The size and shape of the element is chosen to correspond to the desired perforation dimensions and shape. The puncturing element will be made from a material which does not stick substantially to the heated thermoplastic. As the element punctures the films the heat causes the films to melt and fuse at the periphery of the perforation. Closely spaced parallel rows of such perforations are thus made either by using a single element repeatedly or a multiplicity of elements operating in unison. After the perforation is formed the element is withdrawn from the hole and the fused periphery is allowed to cool and solidify.

After the fused peripheries cool the hole-bonded sheets are annealed. The annealing conditions should be such that the sheets shrink at least about 5%. The amount of shrinkage along with the row spacing affects the amplitude of the corrugated ridges. The annealing temperature will be between the glass transition temperature and melting point of the polymer involved. The particular temperature used may also depend on the thermal and mechanical history of the polymer. A substantially crystalline polypropylene film uniaxially oriented to an 8:1 draw ratio shrinks 9% at 250 F., 15% at 275 F. and 43% at 300 F. The annealing may be done conveniently by placing the bonded sheets in a heated oven or bath for the desired time. The shrinkage will usually take less than about 2 minutes; however, longer annealing times may be used if desired.

If the laminated film is used for packaging materials not subject to heat degradation, the laminated film may be first formed around the material and then annealed.

The articles of this invention may be more fully understood by referring to the attached drawing. This drawing illustrates a section of a corrugated article made from two sheets, A and B, cross lapped such that their directions of orientation are rotated 90. Sheet As direction of orientation runs horizontally and Bs mns vertically. The vertical rows of perforations, 1, run along the bottom of the grooves of Sheet As corrugations. correspondingly, the horizontal rows of perforations, 2, run along the grooves of Sheet Bs corrugations.

EXAMPLES The following examples illustrate the corrugated articles of this invention and the method used to make 3 them. These examples are in no manner intended to limit the invention described herein.

Corrugated articles of this invention were prepared using the following general procedure. 1 ft. square pieces which run substantially along the bottoms of the corrugation grooves and fusion bonded at the periphery of each perforation.

2. Article of claim 1 wherein the polymer is a subof 1.9 mil thick uniaxially oriented polypropylene films 5 stantially crystalline poly-l-alkene of monomers con- (draw ratio of 8:1) were cross lapped at 90 relative taining 2to 6 carbonatoms. to their orientation directions. The films were perforated 3, Article of claim 1 wherein the polymer is sub- 1n the deslred pattern by repeatedly plaslng the clrc ular stantially crystalline po1ypmpy1ene P Of a 40 Watt Soldering at 450 to 500 4. Article of claim ,1 wherein the number of sheets is through the films. Care was taken to hold the films close h r t th th h 1 d 1 1 f b h fil mt e range of 2 and 4,.1nclus1ve.

Oge so at t 6 me te Po ypropy em 0 0t ms 5. Article of claim 1 wherein the number of sheets was in contact. The hole-bonded films were then anis 2 nealed by placing them in a forced draft oven at the desired temperature for one-half hour. The strength and t i claim 1 Wherem the sheets are about elongation properties of the resulting corrugated sheets a were evaluated by ASTM D 1682-64. For comparison, Artfcle of 1 Wherem the angle is abPut 90 similarly prepared hole-bonded films which were not an- Artlcle of a 1 Whfirem the Perforatlons l nealed were also evaluated for strength and elongation. clrcular f Y diameters 1n the range of about The particulars of these preparations and evaluations are to about lnchreported in the table below, 9. Article of claim 1 wherein the distance between ad- Laminate construction Hole spacing Article evaluation test Between Between Number rows of holes in Breaking of film Hole holes, in. row, in. Breekmg ngalayers in size, Hole I Annealing loa tron, laminate mm. Ver. Her. Ver. Hor. pattern temp., F. pounds percent Example No.1

1 2 1 0.25 0.25 0.25 0. Square 0 2 1 0. 25 0. 25 0. 25 0. 25 do 200 103 12 2 1 0.25 0. 25 0. 25 0. 25 do 250 128 18 2 1 0.5 0.5 0.25 0. 25 Staggered... 2 1 0. 5 0. 5 0. 25 .do 200 13 2 1 0. 5 0. 5 0. 25 250 107 18 2 1 0.5 0.5 0.5 77 9 2 1 0. 5 0. 5 0. 5 250 125 21 2 2 0. 25 0. 25 0. 25 60 9 2 2 0. 25 0. 25 0. 25 200 55 10 2 2 0. 25 0. 25 0. 25 250 82 1s 2 2 0.5 0.5 0. 25 62 7 2 2 0. 5 0. 5 0. 25 200 75 11 2 2 0.5 0.5 0. 25 250 84 10 2 2 0.5 0.5 0.5 74 10 2 2 0. 5 0. 5 0. 5 250 19 4 1 0. 25 0. 25 0. 25 250 227 25 1 Not annealed.

The above table shows that the corrugated articles of this invention have better strength and elongation properties than corresponding non-corrugated laminates. Cor- 45 rugated articles of this invention are useful in packaging applications such as shrink packaging where the corrugations may be formed during packaging.

As will be evident to those skilled in the art, various modifications on this invention can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the following claims.

I claim:

1. Corrugated thermoplastic article comprising at least two uniaxially oriented sheets of substantially crystalline thermoplastic polymer, said sheets being cross lapped at an angle of at least about 10 relative to their orientation directions, perforated in closely spaced parallel rows jacent perforations in a row is substantially the same as the distance between adjacent rows.

10. Article of claim 9 wherein the distance between adjacent perforations is about 0.1 inch to 3 inches.

References Cited UNITED STATES PATENTS 2,609,956 9/ 1952 Stevenson 161135 2,642,372 6/1953 Chittick 161-109 3,041,223 6/ 1962 Sage 16l135 JOHN T. GOOLKASIAN, Primary Examiner W. E. HOAG, Assistant Examiner US. Cl. X.R. 161-135; 22942 

